The present invention relates to a battery of primarily lead acid type comprising means for indicating the charge or discharge state of the battery.
Electro-chemical storage batteries are used in many applications and in a particular as starter batteries for powering the starter motor of a motor vehicle having an internal combustion engine. A battery conventionally comprises several electrolytic cells electrically connected in series with each other and containing plates submerged in an electrolyte. Batteries of this kind are disclosed in the published International patent applications WO 95/35228 and WO 96/11817 and in the published European patent application EP 0 692 413. In the batteries described in those patent applications an electrical control switch is connected between the middle cells of the batteries. The switch is controlled by electrical circuits protecting the vehicle from theft in which the battery is applied. In the cited International patent application WO 96/11817 also circuits are disclosed for monitoring the discharge and recharging currents of the battery, in particular for calculating and indicating the charge state of the battery, i.e. how much electrical energy there is still stored in the electrochemical system of the battery. Batteries having indication systems for the charge state are also frequently used in small electrically powered devices such as electrically powered razor devices and mobile telephones.
In the published European patent application 0 356 461 and U.S. Pat. No. 5,496,659 batteries having discharge or charge state indication are disclosed. In U.S. Pat. No. 4,675,255 and the German published patent application 36 28 600 external devices for monitoring the charge state of a battery are disclosed.
It is an object of the invention to provide a storage battery having a circuit for indicating the capacity state of the battery, which circuit is easily connected in a battery.
A storage battery of the conventional kind for supplying power to electrical devices comprises a supervising circuit or unit for determining the remaining electric capacity of the battery. The supervising unit is electrically connected to terminal posts of the battery in order to measure the battery voltage and is also arranged to measure the battery current. Therefor, the supervising unit is arranged to determine or measure the voltage over a portion of one of the terminal posts, this portion being used as a known series resistance of the cells of the battery. From this latter voltage the current through the battery is calculated and therefrom the remaining electric capacity of the battery is determined. The voltage indicating the battery current can be measured between a connection of the terminal post to the plates of the responsive cell of the battery and a position somewhere close to an exterior end of the terminal post, e.g. at the location, at which is passes through the lid or the case of the battery. Practically, measurement posts can be arranged, which are connected to the two end cells of the battery in parallel to the terminal post. Then, the supervising unit is connected to the measurement posts and measures the voltage between the two measurement posts or between a measurement post and some position on the terminal post connected parallel to the measurement post.